1. Field of the Invention
The present invention relates to the manufacture of fibers, compositions, products and films from cellulose fiber material, the process for manufacturing these fibers, compositions, products and films and products obtained.
2. Background of the Art
Each year, farming and agricultural processing industries generate millions of tons of by-products. In Minnesota and other Midwestern states, for example, where corn, soybean and sugar beets are the major agricultural crops, producers and processors are facing serious problems in dealing with the large amounts of processing by-products such as sweet corn cobs and husks, soybean hulls, and sugar beet pulps. Some of the by-products are used for land application. Animal feed processing industries consume only a small portion of these by-products, much of these by-products cannot be utilized and hence become wastes, which have to be disposed of at great expense to producers and processors. This situation has significant negative impact on the development of farming and agricultural processing industries as well as the environment. It would be advantageous for the growers, processors, and the environment, if the by-products could be utilized on-site or elsewhere.
The benefits of utilizing agricultural fibrous by-products are two fold. First, value is added to the products and hence to the farming and agricultural processing industries, and second, the products could be 100% biodegradable and free of materials which would persistently and adversely affect the environment. The products would therefore be environmentally friendly. However, lack of technology suitable for processing agricultural by-products into value-added products has been the major obstacle to the utilization of these materials.
There are growing interests expressed by crop growers and processors as well as consumers in 100% biodegradable materials made from agricultural and food industrial by-products. To utilize the by-products generated from agricultural and food industries, new technology is required.
Agricultural growers and food processors will certainly benefit from utilization of their by-products in at least two ways. First, they will gain profit from selling the commodities made from the by-products, such as sweet and yellow dent corn cobs and husks, soy hulls, and sugar beet pulps. Second, the ever increasing cost spent on disposal of the processing by-products, such as sweet corn cobs and husks, oat fibers, soy hulls, and sugar beet pulps, will be greatly reduced. Utilization of agricultural and food industry by-products will have significant impact on our environment. First, the amount of by-products disposed of will be largely reduced. Second, the products made from these by-products are expected to be 100% biodegradable and hence environmentally friendly. Biodegradable products are always welcome and demanded. For example, 100% biodegradable and environmentally friendly materials are strongly demanded by governmental agencies. The U.S. Navy is seeking materials that are 100% biodegradable to make cutlery, dishes, plates and containers, which can be disposed into the seas after use without causing long term pollution.
Many of the food and agricultural byproducts contain substantial amount of cellulosic fibers. Cellulose is the most abundant organic material on earth, and the most important basic molecular unit of plant fibers whose mechanical properties reflect the mechanical characteristics of the plant tissues (Falk, S., Hertz, C. H. and Virgin, H. I. 1958. Physiol. Planetarium 11:802; Frey-Wyssling, A. 1952. Deformation and flow in biological systems. Interscience Publishers, Inc. New York.; Parrott, M. E. and Thrall, B. R. 1978. J. Food Sci. 43:759.). Cellulose has presented its great usefulness in chemical, chemical engineering, paper making, textile, material and food industries over the years. The major challenge these industries are facing is to find ways to extract cellulose from natural materials or synthesize cellulose from chemicals, and to invent methods to make the cellulose into functional products.
Morphologically, plant fibers are formed by fibrils that are composed of microfibrils. Therefore, the microfibrils, bundles of cellulose chains, are the real morphological units of plant material (Mohesinin, N. N. 1986. Physical properties of plant and animal materials. Gorden and Breach Science Publications. New York). Microfibrils display a number of physical and chemical properties associated with strong mechanical strength and chemical inertness (Krassig, H. A. 1993. Cellulose: Structure, accessibility and reactivity. Yverdon, Switzerland.). Microfibrillation of crude fibers through high pressure shearing renders a much stronger mechanical strength to the microfibrillated materials. Many agricultural crops, although composed largely of fibers, appear to have a loose structure and soft texture. When beaten or refined by traditional chemical and mechanical processes, they tend to produce pulp that has low mechanical strength when made into paper and fiberboard. Microfibrillation would be one of the solutions to make mechanically strong and chemically inert materials from fiber-rich food and agricultural by-products.
A process of making microfibrillated cellulose (MFC) from wood pulp was reported by Turbak, A. F., Snyder, F. W. and Sandberg, K. R. 1983a, Turbak, A. F., Snyder, F. W. and Sandberg, K. R. 1983b, U.S. Pat. No. 4,374,702, Turbak, A. F., Snyder, F. W. and Sandberg, K. R. 1983c. J. Appl. Polymer Sci. symposium No.37., 815; Turbak, A. F., Snyder, F. W. and Sandberg, K. R. 1983c. U.S. Pat. No. 4,341,807; Turbak, A. F., Snyder, F. W. and Sandberg, K. R. 1984. U.S. Pat. No. 4,452,721. (What format for listing cited literature?). The potential applications of MFC in foods, paints, pharmaceuticals and cosmetic products have been recognized (Turbak et al., supra), but there has been no recognition of the potential for structural materials, including self supporting films, wrapping materials, and structural support members (e.g., structural ribs, beams, etc.). Moreover, MFC is not commercially available.
The process described by Turbak et al. (U.S. Pat. No. 4,374,702) for preparation of MFC from wood pulp basically involved a homogenization operation, during which wood pulp was repeatedly passed through a high pressure homogenizer until the suspension becomes a substantially stable dispersion. The homogenizer had a small diameter orifice in which the suspension was subjected to a pressure drop of at least 2000 psi and a high velocity decelerating impact against a solid surface. Homogenization is a very efficient process that converts the fibers into microfibrillated cellulose without substantial chemical change of the starting material. Finely divided cellulose is also produced in traditional processes used in manufacturing mechanical pulp, fiberboard and paper pulp. However, these traditional processes involve the use of additional chemical treatment to available cellulose pulps, as for example, acid hydrolysis or mercerization, which chemically alter or degrade the prepared cellulose pulps. In the paper industry, it is well known that paper strength is directly related to the amount of beating or refining which the fibers receive prior to formation. However, beating and refining as practiced in the paper industry are relatively inefficient processes since large amounts of energy are expended to gain relatively minor amounts of fiber opening fibrillation.
The process of U.S. Pat. No. 4,374,702 used wood pulp as a starting material. To be able to process agricultural by-products, additional steps prior to homogenization have been shown to be required (Ruan, R., Y. Lun, J. Zhang, P. Addis, and P. Chen. 1996. Structure-Function Relationships of Highly Refined Cellulose Made from Agricultural Fibrous Residues. Applied Engineering in Agriculture. 12(4):465-468.). The properties of the cellulosic products made from non-wood materials, which may differ from those of the products made from wood materials should be understood.
Edible or Biodegradable Packaging Materials--Films and Coatings
Ordinary food packages use metal, glass, plastic, foil and wax board containers for protection against external contamination, the effects of atmospheric oxygen and moisture, and for protection against mechanical damage. The food is removed or separated from the package at the time of use. In contrast, when package, in the form of film or coating, is an integral part of the food and consumed as such, the package is classified as soluble or edible. The most familiar example of edible packaging is sausage meat in casing that is not removed for cooking and eating. Other examples will be given later.
The primary purpose of packaging in general is to retard undesirable migration of moisture, grease or oil, and gaseous components (oxygen, CO.sub.2, volatile flavors), prevent the food from microbial invasion, mechanical damage and breakage, and isolate reactive ingredients. Additional benefits from edible packaging materials as opposed to ordinary packaging materials are summarized as follows
they are edible, PA1 their cost is generally low, PA1 their use could reduce waste because, PA1 they are part of integrated foods, and biodegradable, PA1 they can enhance the organoleptic, mechanical, and nutritional properties of foods they are suitable of wrapping of small pieces or portions of food, PA1 they can be used inside a heterogeneous food, providing a barrier between components. PA1 environmental legislation, PA1 expanding distribution channels, PA1 consumer expectations for a variety of fresh foods, PA1 need for extended shelf life foods, PA1 opportunities for new foods with edible barriers. PA1 providing a composition comprising non-wood cellulose fiber, PA1 mechanically reducing the size of the cellulose fiber to less than 2 mm (or less than 1 mesh), PA1 reducing the binding effect of lignin on the microfiber content of the cellulose material (which is done by expanding the fibers into microfiber components, essentially breaking the binding action of the lignin on the microfibers, and/or by actually amount of lignin present in said composition comprising cellulose fiber) to form a first fiber product, PA1 providing pressure of at least 300 psi (or at least 500, 750, 1000, 2000 or more psi) to said first fiber product while it is in the presence of a liquid, PA1 removing said pressure within a time interval which will cause said cellulose fiber to break down into a second fiber product comprising microfibers in said liquid, and PA1 optionally hardening said second fiber product by removal of at least some of said liquid. PA1 providing a composition comprising cellulose fiber from at least one plant selected from the group consisting of corn, soy, wheat, whey, peanuts, straw, hay, leaves (from trees), beet pulp, and beets, PA1 mechanically reducing the size of the cellulose fiber to less than 30 mesh, PA1 reducing the amount of lignin present in said composition comprising cellulose fiber to form a first fiber product, PA1 providing pressure of at least 2000 psi to said first fiber product while it is in the presence of a liquid, PA1 reducing said pressure within a time interval which will cause said cellulose fiber to break down into a second fiber product comprising microfibers in said liquid, and PA1 hardening said second fiber product by removal of at least some of said liquid.
These additional benefits, together with the following factors have stimulated the interest in edible packaging:
Examples of applications of edible packaging in food and other products are given in Table 1. The functions of edible packaging are also demonstrated through these examples.
TABLE 1 ______________________________________ Examples of Applications of Edible Packaging in Food and other Industries Products Use and Functions of Edible Packaging ______________________________________ Fresh produce coating - retard moisture transmission, provide protection from mechanical damage, naturally regulate oxygen and carbon dioxide condition to control respiration Dried fruits coating and wrapping - maintain desirable moisture content, prevent stickiness and clumping Dried nuts coating - serve as barrier to oxygen and water to prevent oxidation and moisture absorption, bind flavors, salts, spices, colors and antioxidants Meat and fish wrapping and coating - prevent oxidation, moisture loss and contamination, maintain freshness Cereal foods coating - prevent moisture migration from one component (i.e. raisins) to other component (i.e. corn flakes), carry flavors Bakery foods coating - inhibit moisture penetration and oxidative deterioration, Confectionery coating and wrapping - prevent stickiness and clumping, inhibit oil migration, Powders encapsulation - prevent caking Pharmaceuticals macro- and micro-encapsulation - prevent moisture absorption and oxidation, allow controlled release Flavors encapsulation - prevent gas exchange, inhibit evaporation and oxidation, allow controlled release ______________________________________
Edible films and coatings can be divided into several groups depending on the components that form the main matrix of the edible materials, namely, (1)lipid-based, (2)protein-based, (3)carbohydrate-based, and (4) composite films and coatings. The most important properties of edible films and coatings are the water vapor permeability (WVP) and mechanical properties, namely tensile strength, puncture strength, and flexibility. Each of the edible packaging materials mentioned above has unique properties that are governed by its composition and manufacturing conditions it experienced. For example, lipid-based films have low WVP and mechanical strength, while the protein- and carbohydrate-based films are strong but have higher WVP. Composite films, which may compose of proteins and lipids or mixture of carbohydrates and lipids, have a lower WVP than protein- and carbohydrate-based films and a stronger mechanical strength than lipid-based films. Composite films can be further divided into two types based on the structural relationship between the lipids and the hydrophilic components (proteins and polysaccharides). These two types are namely laminated or bilayer films, in which the lipid is a distinct layer within the films, and emulsified films, in which the lipid is uniformly dispersed throughout the films. The preparation of bilayer films involves four stages: two coating and two drying stages. This is the reason why bilayer films are not popular in food industry although they are good moisture barriers (Debeaufort and Voilley, 1995).
Edible plasticizers are normally incorporated into edible films and coatings to improve the flexibility, machinability and applicability of the edible films and coatings. The mostly used and most suitable plasticizer is glycerol because its edible, water-soluble, polar, nonvolatile, and protein and cellulose miscible nature. The materials of the present invention may also be used effectively as coating compositions (which are biodegradable and even nutritional) for seeds. Individual seeds or small packets of seeds may be coated or bound by the compositions of the present invention. These compositions are able to provide protective coatings that can reduce effects of ambient moisture, dry conditions, pests, mold, fungi and the like. The coating composition may contain repellant additives, fertilization enhancing compounds, and the like. The properties of the coating may be controlled so that modest amounts of moisture will not cause the seeds to germinate, but that normal soaking as occurs in wet fields will allow the seeds to germinate after the coating dissolves or is dispersed. Fertilizer or other plant nutrients specific to the desired seed may be added to the coating to enhance its utility.
100% Biodegradable Molded Articles
Cellulose is a polymer made by plants. Processing of plant cellulose-based polymers into products is a new field, and no references can be found in the scientific literature. However, looking into the techniques for synthetic polymer or plastic processing would be a good starting point.
Molding including injection molding and compression molding is the most common method to produce plastic products from polymers. Both methods are well reviewed and compared by Tucker (1987) and Morton-Jones (1989) (Tucker III, C. L. 1987. In Injection molding and compression molding fundamentals. ed. by A. I. Isayev, pp481. Marcel Dekker, Inc., New York.; and Morton-Jones, D. H. 1989. Polymer Processing. Chapman and Hall, London). Injection molding is characterized by ease of material handling and automation, high production rates and accurately sized products compared to compression molding. However, in cases where the materials possess certain properties which would not work well with injection molding, or injection molded products would not meet the requirements, compression molding becomes a favorable choice.
Compression molding is the oldest mass production process for processing polymers. It is almost exclusively used for thermosets. Compression molding is relatively simple with little scrap produced and low orientation in the moldings, as compared with injection molding. The low orientation feature gives compression molded products many advantages compared to those made using injection molding: (1) fibrous fillers are well distributed and are not disturbed or orientated during processing; (2) the product has low residual stresses; (3) mechanical and electrical properties are retained because there is little shearing flow to cause tracts; (4) mold maintenance is low; and (5) capital and tooling costs are relatively low. Besides, compression molding flows involve modest amounts of deformation, and there are no regions of very high stress, such as at the gate of an injection mold. Consequently, reinforcing fibers are not damaged by the flow during mold filling as often happens in injection molding. Thus, higher concentrations of reinforcing fibers and longer fibers can be included in compression molded materials. There are several stages in the compression molding: (1) positioning of the mold; (2) material preparation; (3) prefill heating; (4) mold filling; (5) pressing; (6) in-mold curing; and finally (7) part removal and cool-down. Recent work in compression molding has focused on the critical issues of mechanical property control, surface finish, cycle time, mold design, and process automation. For compression molding of plant cellulose based polymers containing moisture, new problems will be encountered. A major challenge will come from the design of the mold that allows escape of water during molding and accurate control of the size of the final products. There is no doubt that modified processing procedures and molds can be developed to deal with the particular properties of HRC.
Injection molding will face similar modifications to work optimally with HRC. For injection molding, the flow properties and behaviors of polymers are extremely complex and influential on the process, which are influenced not only by the type of polymeric materials but also the geometrical design of the mold, variables concerning injection, filling, packing and holding. One should realize that in general, plant cellulose based polymeric materials have poor thermal plastic properties, and do not flow well during the molding process, which limits the use of injection molding for processing of this type of material.
Blending in the injection molding process has been used to produce products with new properties. The flow and mechanical properties of a polymer may be improved by blending with other polymer(s). Introduction of synthetic polymers into starch is to impart desirable physical properties, and produce commodities with higher biodegradability. Taking a similar approach, it is possible to blend biodegradable thermal plastic polymers such as polycaprolactone (PCL, a fully biodegradable polyester, polyvinyl alcohol, etc.) into plant cellulose based polymeric materials to improve the performance when subjected to injection molding.